The present invention generally relates to a method of forming a dual-layer anti-reflective coating, and more particularly to form a scum-free anti-reflective coating.
Microcircuit fabrication requires that precisely controlled quantities of impurities be introduced into tiny regions of the silicon substrate, and subsequently these regions must be interconnected to create components and VLSI circuits. The patterns that define such regions are created by lithographic process. As semiconductor devices become more highly integrated, the line width of VLSI circuits is typically scaled down. The semiconductor industry""s drive toward integrated circuits with ever-decreasing geometry, coupled with its pervasive use of highly reflective materials, such as polysilicon, aluminum, and metal silicides, has led to an increase in photolithography-patterning problems. Unexpected reflections from these underlying materials, during the photoresist pattering step, result in the photoresist pattern being distorted. This problem is further compounded when the photolithographic process employs a light source in the ultraviolet (UV) or deep ultraviolet (DUV) ranges. The resulting patterns generated in the photoresist are easily compromised by the effects of uncontrolled reflections from the underlying materials due to the increased optical metallic nature of underlying reflective materials at these wavelengths. Therefore, the fabrication of advanced integrated circuits with submicron geometry is limited.
Hence, an anti-reflective coating (ARC) is needed to solve these problems. However, the effects of the anti-reflective coating are affected by some parameters. The thickness and optical characters of the anti-reflective coating are the major factors that influence the effects. The optical characteristics of the anti-reflective coating include the refractive index (n) and extinction coefficient (k). Further, the thickness and optical characteristics of the anti-reflective coating are affected by materials and recipes used to form the anti-reflective coating.
In order to overcome the disadvantages described above, inorganic anti-reflection material, mainly consisting of silicon oxynitride (SiOxNy), are naturally applied for lithographic application, especially in the deep ultraviolet (DUV) wavelength range. Steps of fabricating silicon oxynitride layer include injection of a preferable gas such as SiH4 and N2O, and controlling the injection rate. Further, plasma is introduced to enhance the formation rate of the silicon oxynitride layer. Nevertheless, a wet etching process is necessary for removing inorganic ARC from a substrate. Furthermore, the silicon oxynitride layer is unlikely to be formed on an organic layer. An example of the prior arts can be found in SPIE Vol. 1674 Optical/Laser Microlithography V, 1992, pp. 350-361, in which Yurika Suda et al. published a paper entitled, xe2x80x9cA New Anti-reflective Layer for Deep UV Lithographyxe2x80x9d. In this paper, an anti-reflective layer (ARL), i.e. an anti-reflective coating, is used for sub-half-micron and quarter-micron KrF excimer laser lithography and has advantages including improved critical dimension (C.D.) control with the photoresist thickness and reduction of notching caused by reflection from the substrate. An a-C:H ARL is underneath the photoresist, and the most suitable film conditions are determined by experimentation. Besides, the a-C:H ARL is organic and can be simultaneously removed with the photoresist. Also, since the exposure and focus latitudes are high, the new scheme is promising for single-layer photoresist processing with KrF excimer laser lithography. However, the organic ARC is not good for later etching, which is due to the varying thickness of the organic ARC resulting from its planar surface.
There are still other issues that need to be solved. For example, some chemical compositions of the ARC will interact with photoresist or the layers under the ARC. This results in scum at the edge of patterned pattern. The critical dimension (C.D.) will be lost because of the scum.
Therefore, what is needed is a novel material for serving as the ARC, which is conformal and can be easily removed from substrates by using conventional dry etching process. Moreover, the optical characters of the ARC are preferably tunable and the material of the ARC is preferably stable with the photoresist thereon or the films thereunder.
The present invention provides a method of forming a dual-layer of anti-reflective coating.
Another object of the present invention is to provide a method of forming the anti-reflective coating with tunable refractive index (n) and exaction coefficient (k).
A further object of the present invention is to provide a method of forming the anti-reflective coating with good conformity.
First, a thin film layer is formed on the substrate, an anti-reflective coating layer is formed on the thin film layer and a photoresist layer is formed on the anti-reflective coating layer. The anti-reflective coating layer is composed of the first layer with a thickness of about 100 to 1000 angstroms and second layer with a thickness of about 100 to 1000 angstroms. The recipe of the first layer includes organic halide (CxHyXz), hydrogen halide (HX), and carrier gas. The refractive index (n) of the first layer is about 1.5 to 2.6 and the extinction coefficient (k) is about 0.1 to 0.9. The recipe of the second layer includes organic halide (CxHyXz) and carrier gas. The refractive index (n) of the second layer is about 1.1 to 2.0 and the extinction coefficient (k) is about 0.01 to 0.5. Next, the photoresist layer is processed by photolithography and the anti-reflective coating layer and thin film layer are anisotropically etched while using the patterned photoresist layer as a mask. Finally, the photoresist layer and the anti-reflective coating are removed by using a conventional dry etching process.